CN107110921B

CN107110921B - MLU-based magnetic sensor with improved programmability and sensitivity

Info

Publication number: CN107110921B
Application number: CN201580073510.4A
Authority: CN
Inventors: S.班迪伊拉
Original assignee: Crocus Technology SA
Current assignee: Crocus Technology SA
Priority date: 2015-01-16
Filing date: 2015-12-23
Publication date: 2020-02-07
Anticipated expiration: 2035-12-23
Also published as: EP3045927A1; JP2018503824A; WO2016113618A1; EP3045927B1; JP6864623B2; US20180003781A1; US9995798B2; CN107110921A

Abstract

The present disclosure relates to a magnetic sensor device for sensing an external magnetic field, comprising a plurality of MLU cells, each MLU cell comprising a magnetic tunnel junction comprising a sense layer having a sense magnetization freely orientable in an external magnetic field, a storage layer having a storage magnetization, and a tunnel barrier layer between the sense layer and the storage layer; the magnetic sensor device further comprises a stress inducing device configured for applying an anisotropic mechanical stress on the magnetic tunnel junction so as to induce a stress induced magnetic anisotropy on at least one of the sensing layer and the storage layer; the stress-induced magnetic anisotropy induced by the stress-inducing device substantially corresponds to a net magnetic anisotropy of the at least one of the sense layer and the storage layer. The magnetic sensor device can be easily programmed and has an improved sensitivity.

Description

MLU-based magnetic sensor with improved programmability and sensitivity

Technical Field

The present invention relates to a Magnetic Logic Unit (MLU) based magnetic sensor device for sensing an external magnetic field, which can be easily programmed and generates a linear signal when an external magnetic field is sensed. The disclosure also relates to a method for programming a magnetic sensor device.

Background

Magnetic Logic Unit (MLU) cells may be used in magnetic sensors or compasses to sense magnetic fields. The MLU cell may include a magnetic tunnel junction including a storage layer having a storage magnetization, a sense layer having a sense magnetization, and a tunnel barrier layer between the storage layer and the sense layer. The sense magnetization can be oriented in the presence of an external magnetic field while the storage magnetization remains substantially undisturbed by the external magnetic field. The external magnetic field can thus be sensed by measuring the resistance of the magnetic tunnel junction, which depends on the relative orientation of the sense and storage magnetizations as oriented by the external magnetic field.

Ideally, the sensing layer has a linear and non-lagging behavior when oriented by an external magnetic field, in order to facilitate measurement of small changes in the external magnetic field. This is relevant when sensing the earth's magnetic field with an average value of about 0.5 oersted (Oe).

Such linear and non-hysteresis behavior may be achieved by providing a magnetic tunnel junction in which the sense magnetization magnetic anisotropy axis is oriented substantially perpendicular to the storage magnetization. This is typically achieved by fixing (pin) the storage magnetization to an anisotropy axis perpendicular to the sense layer. During fabrication of the magnetic tunnel junction, the orientation of the anisotropy axis of the sense layer may be defined by the fabrication conditions (e.g., by applying a magnetic field).

The disadvantages of the above MLU cell are: the anisotropy of only one direction on a wafer comprising a plurality of MRAM cells may be defined by the sputtering regime. Thus, the sense layer magnetization 210 can be oriented perpendicular to the storage magnetization 230 in only one direction in the plane of the sensor device.

Fig. 3 illustrates a conventional MLU-based magnetic sensor device 100 comprising a plurality of MLU cells electrically connected in series to a current line 3. Magnetic sensors typically require at least two sensing directions. Fig. 1 shows a conventional MLU cell comprising a magnetic tunnel junction 2, the magnetic tunnel junction 2 comprising a sense layer 21 having a sense magnetization 210, a storage layer 23 having a storage magnetization 230, a storage antiferromagnetic layer 24 and a tunnel barrier layer 22, the storage antiferromagnetic layer 24 fixing the storage magnetization 230 at a low threshold temperature and leaving it free at a high threshold temperature. The sense magnetization 210 is configured to be orientable in an external magnetic field such that the resistance of the magnetic tunnel junction 2, determined by the relative orientation of the sense magnetization 210 and the storage magnetization 230, is varied.

Referring back to fig. 3, the plurality of MLU cells are represented by

dotted patterns

101, 102, 103. The field lines 4 are configured to generate a magnetic field based on an input (field current). In particular, the plurality of MLU cells are configured in

branches

101, 102, 103, each branch comprising a subset of MLU cells. These branches are oriented at an angle of about 0 °, about 45 °, about 90 ° with respect to the axis x. The field line may comprise a plurality of

portions

401, 402, 403, each respectively arranged adjacent to a corresponding one of the

branches

101, 102, 103 of the MLU cell. The

field line portions

401, 402, 403 are configured such that the direction of current flow 41 through each of the

portions

401, 402, 403 has an angular orientation corresponding to the angular orientation of its

corresponding branch

101, 102, 103. Thus, the programming magnetic field 42 is oriented in a direction perpendicular to the respective

field line portions

401, 402, 403 and aligned (align) along the programming direction 260. The intrinsic anisotropy axis of the sense layer magnetization 210 (referred to as the sense intrinsic anisotropy axis 251) and the intrinsic anisotropy axis 252 of the storage layer magnetization 230 (referred to as the storage intrinsic anisotropy axis 252) are defined by sputtering and/or annealing conditions. In the absence of a magnetic field, the sense magnetization 210 is oriented along the sense intrinsic anisotropy axis 251. In FIG. 3, the sensing intrinsic anisotropy axis 251 and the storage intrinsic anisotropy axis 252 are oriented perpendicular to the programming direction 260 in the branch 101 at about 0, at an angle of about 45 in the subset 102 at about 45, and substantially parallel to the storage magnetization 230 in the subset 103 at about 90.

Another disadvantage of conventional MLU-based magnetic sensor devices is that: during programming of the device, i.e. during the step of setting the orientation of the storage magnetization, the storage magnetization 230 can only be aligned in a direction close to the direction of the storage intrinsic anisotropy axis 251. As discussed above, the latter is oriented in a single direction in all branches of the magnetic sensor device, which direction is determined by the manufacturing process of the magnetic sensor device (sputtering conditions, annealing conditions, etc.). Programming the storage magnetization in a direction not close to the anisotropy axis requires a higher programming field than when performing programming in a direction close to the anisotropy axis. In conventional MLU-based magnetic sensor devices it is not possible to generate a programming magnetic field 42 with the programming line 4 that is large enough to program the storage magnetization 230 in a direction that is not close to the anisotropy axis.

To obtain a 2D magnetic sensor device such as the one depicted in fig. 3, the storage layers 23 in the MLU cells 1 comprised in the different branches should be programmed in different directions and for some branches the programming direction 260 will be away from the magnetic anisotropy axis (i.e. there is an angle of more than 10 ° between the programming direction 260 and the magnetic anisotropy axis), resulting in poor programming in these branches. The sensitivity of poorly programmed branches to external magnetic fields is small and usually not large enough to accurately determine the value of the external magnetic field.

US2012075922 discloses a magnetic memory element capable of maintaining high thermal stability (retention characteristics) while reducing a write current. The magnetic memory element includes a magnetic tunnel junction having a first magnetic body including a perpendicular magnetization film, an insulating layer, and a second magnetic body serving as a storage layer including a perpendicular magnetization film, which are sequentially stacked. The thermal expansion layer is disposed in contact with the magnetic tunnel junction portion. The second magnet is deformed in a direction in which its cross section is increased or decreased by thermal expansion or contraction of the thermal expansion layer due to the flow of current, thereby lowering a switching current threshold required to change the magnetization direction.

US2010080048 discloses a magnetic memory cell comprising a piezoelectric material, and provides a method of operating a memory cell. The memory cell includes a stack (stack), and the piezoelectric material may be formed as a layer in the stack or a layer stacked adjacent to the cell. The piezoelectric material may be used to induce transient stress during programming of the memory cell to reduce a critical switching current of the memory cell.

US2002117727 discloses a magnetoelectronics element including a first magnetic layer, a first tunnel barrier layer on the first magnetic layer, a second magnetic layer on the first tunnel barrier layer, and an upper stressed layer (stressed-overlying) on the second magnetic layer configured to modify a switching energy barrier of the second magnetic layer.

Disclosure of Invention

The present disclosure relates to a magnetic sensor device for sensing an external magnetic field, comprising a plurality of MLU cells, each MLU cell comprising a magnetic tunnel junction comprising a sense layer having a sense magnetization freely orientable in an external magnetic field, a storage layer having a storage magnetization, and a tunnel barrier layer between the sense layer and the storage layer; the magnetic sensor device further comprises a stress inducing device configured for applying an anisotropic mechanical stress on the magnetic tunnel junction, thereby inducing a stress induced magnetic anisotropy on at least one of the sensing layer and the storage layer.

The present disclosure also relates to a method for programming a magnetic sensor apparatus, comprising:

using a stress inducing device for inducing a stress induced magnetic anisotropy on at least one of the sense layer and the storage layer; and

aligning a storage magnetization of each of the plurality of MLU cells in a programming direction.

The advantages of the disclosed magnetic sensor device are: the magnetic anisotropy of the sense and storage layers may be oriented in a particular direction for each branch and each layer, so that the programming and sensitivity of each branch (and thus, the magnetic sensor device) will be improved. In fact, each branch is easier to program, since the net magnetic anisotropy of the storage layer is oriented in a direction close to the programming direction. Since the magnetization of the sense layer is oriented perpendicular to the storage layer magnetization, each branch of the magnetic sensor device exhibits a linear and non-hysteresis behavior.

Drawings

The invention will be better understood by means of the description of an embodiment given by way of example and illustrated by the figures, in which:

FIG. 1 shows a magnetic tunnel junction including a storage layer, a tunnel barrier layer, and a sense layer;

FIG. 2 shows the magnetic tunnel junction of FIG. 1, wherein the storage layer is a synthetic antiferromagnet comprising a first storage ferromagnetic layer, a second storage ferromagnetic layer, and an antiparallel coupling layer;

FIG. 3 illustrates a conventional MLU-based magnetic sensor including a first branch, a second branch, and a third branch containing MLU cells;

FIG. 4 illustrates an MLU-based magnetic field direction measurement device, according to an embodiment;

FIGS. 5a to 5d illustrate four possible ways of inducing stress-induced magnetic anisotropy in the y-direction by using stress-inducing devices;

6 a-6 d illustrate four possible ways of inducing a stress-induced magnetic anisotropy in the sense layer that is substantially perpendicular to a stress-induced magnetic anisotropy in the storage layer by using a stress-inducing device; and

fig. 7a and 7b show the way in which anisotropic stresses in the sense and storage layers are induced due to metal lines having a suitable shape and deposited at high temperature.

Detailed Description

Referring to fig. 1, an MLU cell 1 for sensing an external magnetic field includes a magnetic tunnel junction 2, the magnetic tunnel junction 2 including a sensing layer 21, a storage layer 23, and a tunnel barrier layer 22 between the sensing layer 21 and the storage layer 23. The sense layer 21 has a sense magnetization 210 that is freely orientable in an external magnetic field. The storage layer 23 has a storage magnetization 230, the orientation of which remains stable in an external magnetic field. The MLU cell 1 may also include traces (trace) or strip conductors to provide write and read functions. In particular, the current line 3 may be electrically coupled to the MLU cell 1. The MLU cell 1 may include a programming line 4 that extends substantially perpendicular (or parallel) to the current line 3 and is magnetically coupled to the MLU cell 1. The MLU cell 1 may further include a select transistor 8 electrically connected to the MLU cell 1 by a strap 7.

The sense layer 21 may comprise a soft ferromagnetic material, i.e. a material having a relatively low magnetic anisotropy, while the storage layer 23 may comprise a hard ferromagnetic material, i.e. a material having a relatively high coercivity. Suitable ferromagnetic materials include transition metals, rare earth elements, and alloys thereof with or without main group elements. For example, suitable ferromagnetic materials include iron ("Fe"), cobalt ("Co"), nickel ("Ni"), and alloys thereof, such as: permalloy (or Ni80Fe 20); ni, Fe, and boron ("B") based alloys; co90Fe 10; and alloys based on Co, Fe and B. The thickness of each of the sensing layer 21 and the storage layer 23 may be in the nm range, such as from about 0.4 nm to about 20 nm or from about 1 nm to about 10 nm.

Other implementations of the sensing layer 21 and the storage layer 23 are envisaged. For example, either or both of the sense layer 21 and the storage layer 23 may include a plurality of sublayers in a manner similar to that of a so-called synthetic antiferromagnetic layer. FIG. 2 illustrates a magnetic tunnel junction 2 in which the storage layer 23 comprises a synthetic storage layer or Synthetic Antiferromagnet (SAF) including a first storage ferromagnetic layer 231 having a first storage magnetization 234 and a second storage ferromagnetic layer 232 having a second storage magnetization 235. A storage antiparallel coupling layer 233 is included between the first and second storage

ferromagnetic layers

231, 232. The storage coupling layer 233 creates a RKKY coupling between the first and second storage layers 231, 232 such that the second storage magnetization 235 remains antiparallel to the first storage magnetization 234. The two storage

ferromagnetic layers

231, 232 may comprise CoFe, CoFeB or NiFe alloys and have a thickness typically comprised between about 0.5 nm and about 4 nm. The storage coupling layer 233 may comprise a non-magnetic material selected from the group comprising at least one of: ruthenium, chromium, rhenium, iridium, rhodium, silver, copper and yttrium. Preferably, the storage coupling layer 233 comprises ruthenium and has a thickness typically comprised between about 0.4 nm and 3nm, preferably between 0.6 nm and about 0.9 nm or between about 1.6 nm and about 2 nm.

The tunnel barrier layer 22 may include an insulating material or may be formed of an insulating material. Suitable insulating materials include oxides, such as alumina (e.g., Al)₂O₃) And magnesium oxide (e.g., MgO). The thickness of the tunnel barrier layer 22 may be in the nm range, such as from about 0.5 nm to about 10 nm.

The MLU cell 1 may be configured to be written or programmed by a Thermally Assisted Switching (TAS) operation. Referring again to fig. 1, the MLU cell 1 may further include a fixed layer 24, the fixed layer 24 being disposed adjacent to the storage layer 23 and having a temperature within or near the fixed layer 24 at the low threshold temperature T by exchange biasing_LWhere the storage magnetization 230 is stabilized or fixed along a particular direction. Low threshold temperature T_LMay correspond to a temperature below the blocking temperature, the neel temperature, or another threshold temperature. When the temperature is at a high threshold temperature T_HAt (i.e., at a temperature above the blocking temperature), the pinned layer 24 will store magnetization230 are de-pinned or decoupled, thereby allowing the storage magnetization 230 to be switched to the other direction.

As illustrated in FIG. 2, in the case where the storage layer has an SAF configuration, the fixed layer 24 may be adjacent to the first storage ferromagnetic layer 231, thereby being at a low threshold temperature T_LLower fixed first storage magnetization 234 and at a high threshold temperature T_HLeaving it free. The second storage magnetization 235 is not exchange coupled by the pinned layer 24 but remains antiparallel coupled to the first storage magnetization 234 through the storage coupling layer 233. The pinned layer 24 may also be adjacent to the second storage ferromagnetic layer 232 to exchange couple this layer.

The pinned layer 24 includes or may be formed of a magnetic material, and in particular an antiferromagnetic type magnetic material. Suitable antiferromagnetic materials include transition metals and alloys thereof. For example, suitable antiferromagnetic materials include manganese ("Mn") based alloys, such as iridium ("Ir") and Mn based alloys (e.g., IrMn), Fe and Mn based alloys (e.g., FeMn), platinum ("Pt") and Mn based alloys (e.g., PtMn), and Ni and Mn based alloys (e.g., NiMn). In some cases, the barrier temperature of Ir and Mn (or Fe and Mn) based alloys may be in the range of about 90 ℃ to about 350 ℃ or about 150 ℃ to about 200 ℃, and may be less than the barrier temperature of Pt and Mn (or Ni and Mn) based alloys, which may be in the range of about 200 ℃ to about 400 ℃.

In an embodiment, the MLU cell 1 comprises a stress inducing device 6 configured for applying an anisotropic mechanical stress on the magnetic tunnel junction 2, thereby inducing a stress induced magnetic anisotropy 270 on at least one of the sense layer 21 and the storage layer 23.

Magnetostrictive materials develop large mechanical deformations when subjected to an external magnetic field. This phenomenon is due to the rotation of small magnetic domains in the material, which are randomly oriented when the material is not exposed to a magnetic field. The orientation of these small magnetic domains by the imposition of a magnetic field creates a stress field. As the strength of the magnetic field increases, more and more of the magnetic domains orient themselves so that the major axis of their anisotropy is collinear with the magnetic field in each region and eventually reaches saturation. Conversely, changes in the magnetization or magnetic anisotropy axis due to applied stress are also known as the magnetoelastic effect or the vilarie effect.

Thus, applying an anisotropic mechanical stress on the magnetic tunnel junction 2 induces an additional source of magnetic anisotropy, which is referred to as stress induced magnetic anisotropy. Such anisotropic mechanical stress is generated by the stress-inducing device 6. The stress-inducing device 6 may comprise a metal wire or oxide located near the magnetic tunnel junction 2. In an embodiment, the stress inducing device 6 comprises a current line 3 and/or a programming line 4. Alternatively or in combination, the stress-inducing device 6 may comprise additional metal wires, such as straps 7, or any other metal wires adapted for generating suitable mechanical stress. Alternatively or in combination, the stress-inducing device 6 may comprise an encapsulation layer (not shown), such as a dielectric layer encapsulating the MLU cell 1.

The stress-inducing device is further configured such that the stress-induced magnetic anisotropy 270 has a larger magnitude than any other possible contribution of the magnetic anisotropy, such as the magnetic anisotropy induced by the deposition and/or annealing, shape or crystalline anisotropy (hereinafter referred to in the following text as the sensing intrinsic anisotropy 251 of the sensing layer 21 and the storage intrinsic anisotropy 252 of the storage layer 23). The stress-induced magnetic anisotropy in the sense layer 21 will be referred to as the sense stress-induced magnetic anisotropy 271, and the stress-induced magnetic anisotropy in the storage layer 23 will be referred to as the storage stress-induced magnetic anisotropy 272. Thus, the stress-inducing device 6 is configured such that the sensed stress-induced magnetic anisotropy 271 substantially corresponds to the net sensed magnetic anisotropy 281 and the stored stress-induced magnetic anisotropy 272 substantially corresponds to the net stored magnetic anisotropy 282 (see FIG. 4). Here, the net sense magnetic anisotropy 281 corresponds to the sum of the sense intrinsic anisotropy 251 and the sense stress-induced magnetic anisotropy 271, and the net storage magnetic anisotropy 282 corresponds to the sum of the storage intrinsic anisotropy 251 and the storage stress-induced magnetic anisotropy 271. In other words, the sense intrinsic anisotropy 251 may be neglected compared to the sense stress-induced magnetic anisotropy 271, and the store intrinsic anisotropy 252 may be neglected compared to the store stress-induced magnetic anisotropy 272.

Fig. 4 illustrates an example of a magnetic sensor device 100 for measuring a direction of a magnetic field according to an embodiment. The magnetic sensor device 100 includes a plurality of MLU units 1. The configuration of the magnetic sensor device 100 of fig. 4 is similar to the configuration described in fig. 3. The magnetic sensor device 100 comprises a plurality of

branches

101, 102, 103, wherein each branch comprises a subset of the plurality of MLU cells 1 electrically connected in series to a

current portion

301, 302, 303, respectively, of the current line 3. The magnetic sensor device 100 further comprises a programming line 4 configured for delivering a programming field current 41 for inducing a programming magnetic field 42. The program line comprises

program line portions

401, 402, 403, each addressing (address) a

corresponding branch

101, 102, 103, respectively.

More particularly, each

branch

101, 102, 103 comprises an array comprising one or more rows and/or columns of the plurality of MLU cells 1 electrically connected in series to one of the

current lines

301, 302, 303. For example, each

branch

101, 102, 103 may comprise one row of MLU cells 1 or two or more adjacent rows of MLU cells 1. The programming field current 41 may be passed in each

programming line portion

401, 402, 403 separately. Alternatively, the

programming line sections

401, 402, 403 may be electrically connected in series such that the programming field current 41 passes in the

programming line sections

401, 402, 403 at the same time.

In the arrangement of fig. 4, the magnetic sensor device 100 is represented as having a first branch 101 oriented at an angle of about 0 ° with respect to the axis x, a second branch 102 oriented at an angle of about 45 ° and a third branch 103 oriented at an angle of about 90 ° with respect to the axis x. The MLU cells comprised in the first, second and

third branches

101, 102, 103 are addressed by a first, second and third

programming line portion

401, 402, 403, respectively. The first, second and third

program line portions

401, 402, 403 are electrically connected in series, thereby forming a single program line 4 through which a program current 41 passes.

The

programming line portions

401, 402, 403 are configured such that a programming field current 41 flowing in any of the

programming line portions

401, 402, 403 induces a programming magnetic field 42 in a direction substantially perpendicular to the

programming line portions

401, 402, 403 and the

branches

101, 102, 103.

Other configurations of the magnetic sensor apparatus 100 are contemplated. For example, the magnetic sensor device 100 may comprise a plurality of branches such that the average storage magnetization direction 230 of the MLU cell 1 is substantially equally spaced by an angle of about 360 degrees divided by "n", or about 45 °, wherein "n" may be 8.

According to an embodiment, a method for programming a magnetic sensor device 100 comprises the steps of:

using a stress-inducing device 6 for inducing a storage stress-induced magnetic anisotropy 272 on the storage layer 23 such that the storage stress-induced magnetic anisotropy 272 of the storage layer 23 is substantially parallel to the programming magnetic field 42; and

the storage magnetization 230 of the MLU cells 1 included in each subset is aligned in a programming direction 260 (see fig. 4), which programming direction 260 is substantially parallel to the programming magnetic field 42.

The storage magnetization 230 can be aligned in the programming direction 260 by applying a programming magnetic field 42 in the

field lines

401, 402, 403.

Inducing the storage stress induced magnetic anisotropy 272 and/or sensing the stress induced magnetic anisotropy 271 may be performed by inducing a mechanical stress on the storage layer 23 and/or the sensing layer 21. Mechanical stress may be induced by adapting the shape, material properties and manufacturing conditions of the current wires 3, field wires 4, strips 7 or any other metal wires adapted to generate suitable mechanical stress. Alternatively or in combination, the mechanical stress may be induced by adapting the material properties and the manufacturing conditions of the insulating material located in the vicinity of the magnetic tunnel junction 2, such as the dielectric layer encapsulating the MLU cell 1.

In an embodiment, the stress-inducing device 6 may be configured such that the direction of the storage-induced magnetic anisotropy 271 is different for each of the plurality of

branches

101, 102, 103. This may be achieved by orienting the

current lines

301, 302, 303, or the

field lines

401, 402, 403, the strips 7, or any other metal line or insulating layer adapted to generate a suitable mechanical stress in a suitable direction in each branch.

During a programming operation, the storage magnetization 230 of the MLU cell 1 included in each

branch

101, 102, 103 may be aligned in a programming direction 260 that is substantially parallel to the programming magnetic field 42. Thus, the programming direction 260 of the storage magnetization 230 may be substantially parallel to the stress-induced magnetic anisotropy 272 of the storage layer 23 of the MLU cell 1 comprised in each

branch

101, 102, 103. FIG. 4 also reports storing the orientation of the intrinsic anisotropy 251 for comparison.

In an embodiment, the direction of the sense stress induced magnetic anisotropy 271 in the sense layer 21 and/or the direction of the storage stress induced magnetic anisotropy 272 in the storage layer 23 may be adjusted by adjusting the magnitude of the applied anisotropic mechanical stress.

In another embodiment, the strength and direction of the anisotropic mechanical stress is modified by adjusting at least one of the

current lines

3, 301, 302, 303, or the

field lines

4, 401, 402, 403, or the strips 7, or any other metal line adapted to generate a suitable mechanical stress, or the deposition conditions of an insulating layer located in the vicinity of the MLU cell 1. The strength and direction of the anisotropic mechanical stress can also be tuned by selecting a combination of materials with different coefficients of thermal expansion for the metal and/or insulating material forming the electrical stress-inducing device 6.

In an embodiment, the anisotropic mechanical stress applied by the stress-inducing device 6 is between about 1 MPa and 5 GPa.

The direction of the sensing stress induced magnetic anisotropy 271 in the sensing layer 21 may be determined by modifying the sensing magnetoelastic coupling constant λ of the sensing layer 21₁To adjust. The direction of the storage stress induced magnetic anisotropy 272 in the storage layer 23 may also be modified by modifying the storage magnetoelastic coupling constant λ of the storage layer 23₂To adjust.

In an embodiment, the magnetoelastic coupling constant λ is sensed₁And storing the magnetoelastic coupling constant lambda₂With opposite signs. Thus, application of anisotropic mechanical stress causes the sense stress induced magnetic anisotropy 271 of the sense layer 21 to be orientedIs substantially perpendicular to the storage stress induced magnetic anisotropy 272 of the storage layer 23. In a particular arrangement, the magnetoelastic coupling constant λ is sensed₁And storing the magnetoelastic coupling constant lambda₂In a range between about-1000 ppm and about 1000 ppm.

Fig. 5a to 5d show four possible ways of inducing a stress-induced magnetic anisotropy 271 in the y-direction by using a stress-inducing device 6. In fig. 5a to 5d, the magnetic tunnel junction or sensing layer 21 is schematically represented as seen from the top. For positive sensing magnetoelastic coupling constant lambda₁The sense stress induced magnetic anisotropy 271 induced by the stress σ is perpendicular to the stress direction of the compressive stress (σ)_xx>0, see fig. 5 a), and parallel to the stress direction of the tensile stress (σ)_yy>0, see fig. 5 d). For negative sensed magnetoelastic coupling constant lambda₁The sense stress induced magnetic anisotropy 271 is perpendicular to the stress direction (σ) of the tensile stress_xx>0, see fig. 5 b), or parallel to the stress direction of the compressive stress (σ)_yy<0, see fig. 5 c).

Fig. 6a to 6d show four possible ways of inducing a sense stress induced magnetic anisotropy 271 in the sense layer 21 substantially perpendicular to the store stress induced magnetic anisotropy 272 in the storage layer 23 by using the stress inducing device 6. In fig. 6a to 6d, the magnetic tunnel junction 2 is schematically shown as seen from the top. If the magnetoelastic coupling constant lambda is sensed₁And storing the magnetoelastic coupling constant lambda₂With opposite signs, this can be achieved by any combination of direction and sign of the stress σ. In the example of FIGS. 6 a-6 d, a sense stress induced magnetic anisotropy 271 in the sense layer 21 that is substantially perpendicular to a store stress induced magnetic anisotropy 272 in the storage layer 23 passes through the sense magnetoelastic coupling constant λ₁Is negative (<0) And stores the magnetoelastic coupling constant lambda₂Is a reaction of>0) Applying a compressive stress (σ)_xx<0) (fig. 6 a). This is also achieved by applying a voltage at λ₁>0 and lambda₂<0 applied compressive stress (σ)_xx<0) (FIG. 6 b), or by applying a voltage at λ₁<0 and lambda₂>0 tensile stress (σ)_xx>0) (FIG. 6 c), and by applying a voltage at λ₁>0 and lambda₂<0 tensile stress (σ)_xx>0) (fig. 6 d).

Thus, the stress-inducing device 6 is capable of applying anisotropic mechanical stress inducing sensed and stored stress-induced

magnetic anisotropy

271, 272 on the sense layer 21 and the storage layer 23, respectively, wherein the sensed stress-induced magnetic anisotropy 271 of the sense layer 21 has a different direction than the direction of the stored stress-induced magnetic anisotropy 272 of the storage layer 23.

Fig. 7a and 7b show the way in which anisotropic stresses in the sense layer 21 and the storage layer 23 are induced due to the metal lines 7 having a suitable shape and deposited at high temperature. In fig. 7a and 7b, the magnetic tunnel junction 2 and the stress inducing device 6 are schematically shown as seen from the top. In the present example, the stress-inducing device 6 comprises a metal wire 7 having a rectangular shape (in this example, the longer dimension is along the y-axis). The metal wire 7 is deposited at a temperature higher than the operating temperature of the sensor device (fig. 7 a). The working temperature may vary between 0 ℃ and 85 ℃, may be between-40 ℃ and 180 ℃, and may be as high as 250 ℃. The deposition temperature may be between 150 ℃ and 400 ℃, and possibly between 20 ℃ and 800 ℃. The wire 7 is cooled to the operating temperature of the apparatus after the treatment. As can be seen in fig. 7b, the metal wire 7 shrinks due to the thermal contraction of the metal wire 7 (the rectangle in the dashed line shows the dimension of the wire 7 before cooling). Since the metal line 7 has a length (in y) greater than a width (in x), the shrinkage is anisotropic. In other words, the deformation ε in the x-direction_xxLess than deformation in y-direction epsilon_yy. The anisotropic shrinkage induces an anisotropic compressive stress in the y-direction on the magnetic tunnel junction 2 deposited over the metal line 7.

In the case of a TAS-based programming operation, the method may further include the steps of: passing a heating current 31 in the

current lines

301, 302, 303, thereby heating the MLU cells 1 in the

corresponding subsets

101, 102, 103 to highThreshold temperature T_HAnd the storage magnetization 230 of the MLU cell 1 is unfixed. After or simultaneously with the step of aligning the storage magnetization 230 in the programming direction 260, the method may comprise cooling the MLU cells 1 comprised in the

corresponding subset

101, 102, 103 to the low threshold temperature T_LThereby fixing the switched storage magnetization 230 in the programming direction 260.

The sensing operation of the magnetic sensor device 100 comprises passing a sensing current 32 in the

current branches

301, 302, 303, thereby measuring an average resistance R. Here, the average resistance R corresponds to the resistance measured continuously for the MLU cells included in the

branches

101, 102, 103. The resistance of each MLU cell is determined by the relative orientation of the sense magnetization 210 with respect to the storage magnetization 230. The sense magnetization 210 can be varied by passing a sense field current 43 in the

programming line portions

401, 402, 403, thereby generating a sense magnetic field 44. The sense field current 43 may be modified such that the sense magnetic field 44 and the average resistance R are modulated according to the polarity of the sense field current 43. Since the sense stress induced magnetic anisotropy 271 (or induced net magnetic anisotropy 281) is initially substantially perpendicular to the storage stress induced magnetic anisotropy 272 (or stored net magnetic anisotropy 282), the response will be linear.

When the magnetic sensor device 100 is used for sensing an external magnetic field, such as the earth's magnetic field, the sensing magnetization 210 is aligned in the external magnetic field in accordance with the respective orientation of the external magnetic field and the respective orientation of the

branches

101, 102, 103 with respect to the direction of the external magnetic field. The external magnetic field may be determined by passing the sense current 32 in the

current branches

301, 302, 303, such that the average resistance R is measured by passing the sense current 32 in the

current branches

301, 302, 303.

The MLU-based magnetic sensor device 100 disclosed herein may be comprised in a magnetometer and/or a compass, for example.

In one embodiment, the magnetic sensor device 100 may be used to measure the direction of an external magnetic field in two dimensions, such as the earth's magnetic field, for example, the components of the external magnetic field in a two-dimensional plane. Devices incorporating the design principles of the magnetic sensor device 100 can also measure the direction of an external magnetic field in three dimensions, such as by using a magnetic sensor device 100 that utilizes hall effect vertical axis sensing. The hall effect can result in a voltage difference (hall voltage) across the electrical conductor transverse to the current in the conductor and the magnetic field perpendicular to the current. Based on the hall effect, the component of the external magnetic field in the third dimension can be determined.

Reference numerals and symbols

1 MLU Unit

100 magnetic sensor device

101 first subset, first branch

102 second subset, second branch

103 third subset, third branch

2 magnetic tunnel junction

21 sensing layer

210 sense magnetization

22 tunnel barrier layer

23 storage layer

230 storage magnetization

231 first storage ferromagnetic layer

232 second storage ferromagnetic layer

233 storage coupling layer

234 first storage magnetization

235 second storage magnetization

24 anchoring layer

251 sensing intrinsic anisotropy

252 store intrinsic anisotropy

260 programming direction

271 sensing stress induced magnetic anisotropy

272 storage stress induced magnetic anisotropy

281 sense Net magnetic anisotropy

282 storage net magnetic anisotropy

3 current line

301 first current branch

302 second current branch

303 third current branch

31 heating current

32 sense current

4 programming line

401 part of programming line

402 programming line section

403 program line part

41 programming field current

42 programming magnetic field

43 sense field current

44 induced magnetic field

6 stress inducing device

7 additional metal wire

λ₁Sensing a magnetoelastic coupling constant

λ₂Storage of magnetoelastic coupling constants

Stress of sigma

Deformation of epsilon

σ_xxStress in x direction

σ_yyStress in y-direction

ε_xxDeformation in x-direction

ε_yyDeformation in the y-direction

R average resistance

T_HHigh threshold temperature

T_LA low threshold temperature.

Claims

1. A magnetic sensor apparatus for sensing an external magnetic field comprising a plurality of Magnetic Logic Unit (MLU) cells, each MLU cell comprising a magnetic tunnel junction comprising a sense layer having a sense magnetization freely orientable in the external magnetic field, a storage layer having a storage magnetization, a tunnel barrier layer between the sense layer and the storage layer, and

a stress inducing device configured to exert an anisotropic mechanical stress on the magnetic tunnel junction to induce a stress-induced magnetic anisotropy on at least one of the sense layer and the storage layer;

wherein the stress-induced magnetic anisotropy induced by the stress-inducing apparatus substantially corresponds to a net magnetic anisotropy of the at least one of the sense layer and the storage layer; and is

Wherein the stress-inducing apparatus is further configured such that the applied anisotropic mechanical stress induces the stress-induced magnetic anisotropy in the sense layer and the storage layer such that a direction of the sense stress-induced magnetic anisotropy of the sense layer is different from a direction of the storage stress-induced magnetic anisotropy of the storage layer.

2. The magnetic sensor apparatus of claim 1, wherein respective directions of stress-induced magnetic anisotropy of the sense layer and the storage layer are adjustable by adjusting a magnitude of an applied anisotropic mechanical stress.

3. The magnetic sensor device of claim 1, wherein a direction of a sensing stress induced magnetic anisotropy of the sensing layer is adjustable by adjusting a sensing magnetoelastic coupling constant of the sensing layer, and

wherein the direction of the storage stress induced magnetic anisotropy of the storage layer is adjustable by adjusting a storage magnetoelastic coupling constant of the storage layer.

4. The magnetic sensor device according to claim 3, wherein the sensing magnetoelastic coupling constant has a sign opposite to a sign of the storage magnetoelastic coupling constant such that a sensing stress induced magnetic anisotropy of the sensing layer is oriented substantially perpendicular to a storage stress induced magnetic anisotropy of the storage layer when the anisotropic mechanical stress is applied.

5. The magnetic sensor device according to claim 3, wherein said sensed magnetoelastic coupling constant and said stored magnetoelastic coupling constant are in a range between-1000 ppm and 1000 ppm.

6. The magnetic sensor apparatus according to claim 1, wherein the stress inducing apparatus comprises conductive strips comprising a metal and/or an insulating material adapted for inducing the stress induced magnetic anisotropy.

7. The magnetic sensor device according to claim 6, wherein the strength and direction of the anisotropic stress is adjustable by adjusting at least one of: the material properties and deposition conditions of the metal lines and/or oxides forming the stress-inducing device, or the shape of the metal lines.

8. The magnetic sensor device according to claim 6, wherein the strength and direction of the anisotropic stress can be adjusted by selecting combinations of materials with different coefficients of thermal expansion for the metals and/or oxides forming the stress inducing device.

9. The magnetic sensor apparatus according to claim 1, wherein the anisotropic mechanical stress applied by the stress-inducing apparatus is between about 1 MPa to 5 GPa.

10. The magnetic sensor device of claim 1, comprising:

a plurality of branches, each branch comprising a subset of a plurality of MLU cells, each subset electrically connected in series by a current line configured to pass a sense current adapted to sense an average resistance of the subset corresponding to an average orientation of the sense magnetization in each of the plurality of MLU cells in response to the external magnetic field;

wherein the stress inducing apparatus is configured to induce the stress-induced magnetic anisotropy on at least one of the sense layer and the storage layer of each MLU cell of the subset for each branch of the plurality of branches.

11. The magnetic sensor apparatus according to claim 10, wherein each subset is in magnetic communication with a programming line arranged for delivering a field current inducing a programming magnetic field adapted for aligning the storage magnetization of MLU cells comprised in the subset in a programming direction.

12. The magnetic sensor device of claim 10, wherein the stress-inducing device is further configured such that a direction of the induced magnetic anisotropy is different for each of the plurality of branches.

13. A method for programming a magnetic sensor apparatus, the magnetic sensor apparatus comprising a plurality of magnetic logic unit, MLU, cells, each MLU cell comprising a magnetic tunnel junction comprising a sense layer having a sense magnetization freely orientable in an external magnetic field, a storage layer having a storage magnetization, a tunnel barrier layer between the sense layer and the storage layer, and a stress inducing apparatus configured for applying an anisotropic mechanical stress on the magnetic tunnel junction to induce a stress-induced magnetic anisotropy on at least one of the sense layer and the storage layer;

Wherein the stress-inducing apparatus is further configured such that the applied anisotropic mechanical stress induces the stress-induced magnetic anisotropy in the sense layer and the storage layer such that a direction of the sense stress-induced magnetic anisotropy of the sense layer is different from a direction of the storage stress-induced magnetic anisotropy of the storage layer,

the method comprises the following steps:

using the stress-inducing apparatus for inducing stress-induced magnetic anisotropy on the sense layer and the storage layer such that a direction of the sense stress-induced magnetic anisotropy of the sense layer is different from a direction of the storage stress-induced magnetic anisotropy of the storage layer; and

14. The method of claim 13, wherein the aligning storage magnetizations is performed for each branch for MLU cells included in each subset.